Current sensor

ABSTRACT

A current sensor is configured to detect a current flowing through an electrical conductor. The current sensor includes a core and a coil wound around the core. The core has a hollow therein configured to allow the electrical conductor to pass through the hollow. The core substantially has a C-shape having a gap connected to the hollow. The core has a pair of end surfaces facing each other in a facing direction across the gap. The core includes plural split cores joined to one another. Each pair of split cores of the plural split cores adjacent to each other have respective joining surfaces joined to each other. The respective joining surfaces of the each pair of split cores being parallel to the facing direction. This current sensor has a desired sensitivity characteristic.

TECHNICAL FIELD

The present disclosure relates to a current sensor.

BACKGROUND ART

PTL1 discloses a conventional current sensor in which an electricalconductor is disposed to pass through an annular core on which a coil ispartially wound. The annular core of this current sensor is divided inorder to facilitate disposing the electrical conductor inside theannular core. In an assembly process, the electrical conductor is firstdisposed in the divided cores, and then, the cores are assembled suchthat the electrical conductor passes through the annular core.

CITATION LIST Patent Literature

PTL1: Japanese Patent Laid-Open Publication No. 9-166625

SUMMARY

A current sensor is configured to detect a current flowing through anelectrical conductor. The current sensor includes a core and a coilwound around the core. The core has a hollow therein configured to allowthe electrical conductor to pass through the hollow. The coresubstantially has a C-shape having a gap connected to the hollow. Thecore has a pair of end surfaces facing each other in a facing directionacross the gap.

The core includes plural split cores joined to one another. Each pair ofsplit cores of the plural split cores adjacent to each other haverespective joining surfaces joined to each other. The respective joiningsurfaces of the each pair of split cores being parallel to the facingdirection.

This current sensor has a desired sensitivity characteristic.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a current sensor in accordance with anexemplary embodiment.

FIG. 2 is an exploded perspective view of the current sensor inaccordance with the embodiment.

FIG. 3 is a sectional view of the current sensor along line shown inFIG. 1.

FIG. 4 is a perspective view of a sensor unit of the current sensor inaccordance with the embodiment.

FIG. 5 is an exploded perspective view of the sensor unit in accordancewith the embodiment.

FIG. 6 is a plan view of the sensor unit in accordance with theembodiment.

FIG. 7 illustrates a BH curve of ferrite which is material of a core inaccordance with the embodiment.

FIG. 8 illustrates comparison of output waveforms between the core inaccordance with the embodiment and a core of a comparative example.

FIG. 9 illustrates a relationship of a gap of a core and an output ofthe current sensor in accordance with the embodiment.

FIG. 10A is a front view of another core in accordance with theembodiment.

FIG. 10B is a side view of the core shown in FIG. 10A.

FIG. 11 illustrates a current and an output with respect to the core inaccordance with the embodiment.

FIG. 12 is a plan view of still another core in accordance with theembodiment.

FIG. 13 is a plan view of a further core in accordance with theembodiment.

FIG. 14A illustrates an influence of an electrical conductor on a coreof modified example 1.

FIG. 14B illustrates an influence of an electrical conductor on a coreof modified example 2.

FIG. 14C illustrates an influence of an electrical conductor on the corein accordance with the embodiment.

FIG. 15 illustrates the core and an output of the current sensor inaccordance with the embodiment.

FIG. 16 illustrates the core and an output of the current sensor inaccordance with the embodiment.

FIG. 17 illustrates the core and an output of the current sensor inaccordance with the embodiment.

FIG. 18 is a perspective view of another current sensor in accordancewith the embodiment.

FIG. 19 is a sectional view of the current sensor taken along lineXIX-XIX shown in FIG. 18.

FIG. 20 is a sectional view of the current sensor taken along line XX-XXshown in FIG. 18.

FIG. 21 is a perspective view of a housing of the current sensor shownin FIG. 18.

FIG. 22 is an enlarged sectional view of the current sensor shown inFIG. 19.

FIG. 23 is a perspective view of a sensor unit of the current sensorshown in FIG. 18.

FIG. 24 is a perspective view of another sensor unit of the currentsensor shown in FIG. 18.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Exemplary embodiments described below are examples of the presentdisclosure. Numerical values, shapes, materials, components, arrangementand connection style of components, processes, sequence of processes,and the like are merely examples and not intended to limit the intentionof the present disclosure. Still more, components of the exemplaryembodiments that are not described as components in an independent claimindicating an aspect of the present disclosure are described asarbitrary components. Exemplary embodiments of the present disclosureare not limited to the current independent claim, and may be representedby other independent claims.

Exemplary Embodiment Configuration of Current Sensor

FIG. 1 is a perspective view of an outline of current sensor 10 inaccordance with an exemplary embodiment. FIG. 2 is an explodedperspective view of current sensor 10. FIG. 3 is a sectional view ofcurrent sensor 10 taken along line III-III shown in FIG. 1. In FIG. 1,wire electrical conductor W to be detected is indicated with a brokenline. In the following description, an X-axis direction is indicated aswidth direction X, a Y-axis direction is indicated as thicknessdirection Y, and a Z-axis direction is indicated as up-down direction Z.

Current sensor 10 is a current transformer (CT) type current sensorconfigured to detect an alternating-current (AC) current flowing throughelectrical conductor W. Current sensor 10 includes housing 20 and sensorunit 30 accommodated in housing 20.

Housing 20 is made of, for example, non-magnetic resin, andsubstantially has a rectangular parallelepiped shape as a whole. Housing20 has a uniform thickness (a length in the Y-axis direction) as awhole. Housing 20 is divided into cases 21 and 22 in the Z-axisdirection. Case 21 is a part of the housing located in a negativedirection along of the Z axis while case 22 is a part of the housinglocated in a positive direction along of the Z axis.

Case 21 includes main body 211 and a pair of locking parts 212configured to be engaged with case 22. Main body 211 has a box shapehaving space 21 s therein opening in the positive direction along the Zaxis. Main body 211 includes a pair of lower walls 213 facing each otherin the Y-axis direction, a pair of lower walls 214 facing each other inthe X-axis direction, and bottom plate 219. Lower walls 213 and 214 areconnected to one another, and extended from bottom plate 219 in thepositive direction of the Z axis. Lower walls 213 and 214 and bottomplate 219 surround space 21 s. A pair of inner walls 215 parallel tolower walls 213 are provided inside case 21. The pair of inner walls 215are arranged in the Y-axis direction at a predetermined interval betweeninner walls 215. A part of sensor unit 30 is fitted in and fixed betweenthe pair of inner walls 215. Cutout 213 a having a semicircular shape isprovided in each of the pair of lower walls 213. Cutout 215 a having asemicircular shape is provided each of the pair of lower walls 215.

The pair of locking parts 212 are extended from an outer surface of thepair of lower walls 214 in the positive direction of Z axis. Each of thepair of locking parts 212 substantially has a U-shape. Case 21 and Case21 are assembled together and fixed to each other by engaging the pairof locking parts 212 with fitting protrusions 228 a and 229 b providedon case 22.

Case 22 has a box shape having space 22 s therein opening in thenegative direction of the Z axis. Case 22 includes a pair of upper walls223 facing each other in the Y-axis direction, a pair of upper walls 224facing each other in the X-axis direction, and bottom plate 229. Upperwalls 223 and 224 are connected to one another and extended from bottomplate 229 in the negative direction of the Z axis. Upper walls 223 and224 and bottom plate 229 surround space 22 s.

Cutout 223 a having a semi-circular shape is provided in each of thepair of upper walls 223. Cutout 223 a forms through-hole 20 h shown inFIG. 1 together with cutout 213 a provided in case 21 while case 21 andcase 22 are assembled together. Electrical conductor W is inserted inthrough-hole 20 h. In this state, electrical conductor W is disposedalso in cutouts 215 a in the pair of inner walls 215. Cutouts 213 a, 215a, and 223 a functions as supporters supporting electrical conductor W.

A pair of protrusions 224 a sandwiching sensor unit 30 in the Y-axisdirection are provided on an inner surface of the pair of upper walls224, respectively. FIG. 3 only shows one of the pair of protrusions 224a located in the positive direction of the Y axis. The pair ofprotrusions 224 a are extended in the Z-axis direction. The pair ofprotrusions 224 a are disposed in the Y-axis direction at apredetermined interval from each other. A part of sensor unit 30 isfitted between the pair of protrusions 224 a and fixed onto the pair ofprotrusions 224 a.

Regulating projection 224 b that regulates positional deviation ofsensor unit 30 in the up-down direction is provided on the inner surfaceof each of the pair of upper walls 224. Regulating projections 224 b aredisposed between the pair of protrusions 224 a, and extended in theZ-axis direction. A Lower surface of regulating protrusion 224 bcontacts an upper surface of sensor unit 30 so as to regulate positionaldeviation of sensor unit 30 in up-down direction Z with respect tohousing 20.

Three fitting protrusions 228 a and 228 b are provided on the outersurface of each of the pair of upper walls 224. Two fitting protrusions228 b among these three fitting protrusions 228 a and 228 b are providedon a lower end of upper wall 224, and arranged with a predeterminedinterval from each other in the Y-axis direction. Two fittingprotrusions 228 b sandwich locking part 212 of case 21 in the Y-axisdirection. On the other hand, remaining one fitting protrusion 228 a isdisposed on an upper center area of two fitting protrusions 228 b in theY-axis direction. Fitting protrusion 228 b supports an upper part oflocking part 212 of case 21 from below. Three fitting protrusions 228 aand 228 b engaged with locking part 212 in this state restrict relativepositional deviation of case 21 and case 22, and allow case 21 and case22 to be assembled together and fixed to each other.

Sensor unit 30 will be described below. FIG. 4 is a perspective view ofsensor unit 30 in accordance with the embodiment. FIG. 5 is an explodedperspective view of sensor unit 30 in accordance with the embodiment.FIG. 6 is a plan view of sensor unit 30 in accordance with theembodiment.

As shown in FIGS. 4 to6, sensor unit 30 includes core 40, bobbin 50, andcoil 60.

Core 40 is made of magnetic material, such as ferrite, and substantiallyhas a C-shape having hollow 40 h and gap S connected to hollow 40 h.Core 40 has a rectangular frame shape in a plan view. Gap S is providedat the center of an upper frame part of the rectangular frame shape. Across section of four outer corners of core 40 is a sharp corner, and across section of four inner corners is a round corner. However, thecross section of the four outer corners may have an arcuate shape andthe cross section of the four inner corners may be sharp. Still more,the outer shape of core 40 is not necessarily the rectangular frameshape. Other polygonal frames, round frames, oval frames, ellipsoidalframes, or the like are applicable.

Core 40 includes split cores 41, 42, and 43 joined to one another. Splitcore 41 is a lower part of core 40, and split cores 42 and 43 are anupper part of core 40.

Split core 41 substantially has a U-shape with an open top. A pair ofend surfaces of split core 41 face upward. These end surfaces arejoining surfaces 411 and 412 that are joined with other split cores 42and 43. The pair of joining surfaces 411 and 412 are planes parallel toan XY plane including the X axis and the Y axis. Joining surface 411 isdisposed in the negative direction of the X-axis, and joining surface412 is disposed in the positive direction of the X axis.

Split core 42 substantially has an L-shape. One end surface of splitcore 42 is joining surface 421 that is joined with joining surface 411of split core 41. Joining surface 421 of split core 42 is a planeparallel to the XY plane. Joining surface 421 is joined with joiningsurface 411 of split core 41 with other end surface 422 of split core 42directed in the positive direction of the X-axis. Other end surface 422of split core 42 is a plane parallel to a YZ plane including the Y axisand the Z axis.

Split core 43 substantially has an L-shape. Split core 43 is the same assplit core 42. One end surface of split core 43 is joining surface 431that is joined with joining surface 412 of split core 41. Joiningsurface 431 of split core 43 is a plane parallel to the XY plane.Joining surface 431 is joined with joining surface 412 of split core 42with other end surface 432 of split core 43 facing the negativedirection of the X axis. Other end surface 432 of split core 43 is aplane surface parallel to the YZ plane.

Each pair of split cores of split cores 41, 42, and 43 adjacent to eachother have respective joining surfaces parallel to facing direction DX.Other end surface 422 of split core 42 faces other end surface 432 ofsplit core 43 in facing direction DX parallel to the X axis. Gap S isprovided in core 40 between other end surface 422 of split core 42 andother end surface 432 of split core 43. In other words, other endsurface 422 of core 42 faces other end surface 432 of split core 43across gap S in facing direction DX. Distance LX of gap S in facingdirection DX (a length in the X-axis direction) is adjusted beforeassembling current sensor 10 to obtain a desired sensitivitycharacteristic. As described above, both joining surface 411 of splitcore 41 and joining surface 412 of split core 42 are planes parallel tothe XY plane. Therefore, joining surfaces 411 and 421 of split cores 41and 42 slide with respect to each other to move split core 42 and adjustthe position of other end surface 422 of split core 42 in the X-axisdirection. In other words, distance LX of gap S is adjustable. Thisconfiguration also applies to the relationship between joining surface412 of split core 41 and joining surface 431 of split core 43. Inaccordance with the embodiment, a desired sensitivity characteristic isobtained by distance LX of gap S in a state that the outer surfaces ofthe pair of split cores 42 and 43 are flush with the outer surface ofsplit core 41. To achieve the desired sensitivity characteristic, noconductive material is preferably disposed in gap S.

An annular core made of split cores may have a boundary part whenassembled. Since this boundary part has a faint gap, the boundary partaffects current detection and may reduce the sensitivity.

Current sensor 10 in accordance with the embodiment, as described above,provides a desired sensitivity characteristic.

In accordance with the embodiment, both joining surface 411 of splitcore 41 and joining surface 421 of split core 42 are planes parallel tothe XY plane. However, both joining surface 411 of split core 41 andjoining surface 421 of split core 42 may be parallel to the X-axisdirection and inclined with respect to the Y-axis direction. In thiscase, joining surfaces 411 and 421 of split cores 41 and 42 may slide tomove split core 42 and adjust the position of other end surface 422 ofsplit core 42 in the X-axis direction. Both joining surface 411 of splitcore 41 and joining surface 421 of split core 42 may be curved as longas joining surfaces 411 and 421 contact each other with planes.

Bobbin 50 is made of nonmagnetic material, such as resin. Bobbin 50includes bobbin body 51 having a rectangular tubular shape and a pair offlanges 52 each extended from respective one of both ends of bobbin body51 in the X-axis direction. Bobbin body 51 is extended in the X-axisdirection. Coil 60 is wound on bobbin body 51 about winding axis 60 cextended in the X-axis direction. Coil 60 is housed between the pair offlanges 52. A pair of internal spaces 50 s are provided along windingaxis 60 c in bobbin 50, i.e., bobbin body 51.

As shown in FIG. 3, internal bottom part 53 that divides an inside ofbobbin body 51 into the pair of internal spaces 50 s of bobbin body 51is provided at the center of an inside of bobbin body 51. The internalspaces 50 s open on bobbin body at a pair of openings 50 p,respectively. An end part including end surface 422 of split core 42 andan end part including end surface 432 of split core 43 are fitted in thepair of openings 50 p while contacting internal bottom part 53 so as tocontact bobbin body 51. In other words, bobbin 50 contacts and stops thepair of other end surfaces 422 and 432 of core 40, and surrounds gap S.As a result, internal bottom part 53 regulates gap S between other endsurface 422 of split core 42 and other end surface 432 of split core 43.A thickness of internal bottom part 53 (a length in the X-axisdirection) is distance LX of gap S. In other words, the thickness ofinternal bottom part 53 is previously adjusted such that distance LXproviding a desired sensitivity characteristic.

Coil 60 is a conductive wire, and is wound around bobbin body 51 withplural turns. As described above, the end part of split core 42 and theend part of split core 43 are press-fitted into the pair of internalspaces 50 s of bobbin body 51 so that the pair of other end surfaces 422and 432 of core 40 are located inside coil 60.

An operation of current sensor 10 will be described below. When magneticflux is generated inside core 40 by an alternating-current (AC) currentflowing through electrical conductor W, an AC current that cancels themagnetic flux flows in coil 60. A measuring instrument is connected toboth ends of coil 60 so that the measuring instrument detects andmeasures the AC current flowing through electrical conductor W accordingto the AC current flowing in coil 60.

Method of Assembling Current Sensor

A method of assembling current sensor 10 will be described below.Current sensor 10 may be assembled by an operator or an assemblyapparatus. Here, assembly by the operator will be described.

First, the operator prepares bobbin 50 by winding coils 60 around bobbinbody 51 by a predetermined number of turns. The operator fits the endpart of split core 42 and the end part of split core 43 into the pair ofopenings 50 p in bobbin body 51. Here, the operator ensures that endsurface 422 of split core 42 and end surface 432 of split core 43contact internal bottom part 53. This operation allows other endsurfaces 422 and 432 face each other across gap S with distance LX.

Then, the operator assembles the pair of split cores 42 and 43 andbobbin 50 with case 22. More specifically, the operator fits the pair ofsplit cores 42 and 43 and bobbin 50 that are assembled together intobetween the pair of protrusions 224 a from beneath case 22. Here, theoperator slides the pair of split cores 42 and 43 and bobbin 50 withrespect to case 22 until the top end surfaces of the pair of split cores42 and 43 contact regulating projections 224 b of case 22. Thisoperation fixes the pair of split cores 42 and 43 and bobbin 50 insidecase 22. Split cores 42 and 43 are fitted into spaces 50 s until splitcores 42 and 43 contact internal bottom part 53 of bobbin 50 to contactbobbin body 51 in order to be firmly fixed on bobbin 50. Bobbin 50 andsplit cores 42 and 43 are thus easily fixed onto case 22.

The operator assembles split core 41 to case 21. More specifically, theoperator fits split core 41 into between the pair of inner walls 215from above case 21. Here, the operator slides split core 41 with respectto case 21 until the bottom end surface of split core 41 contacts aninternal bottom of case 21. This will fix split core 41 inside case 21.

Next, the operator assembles electrical conductor W to case 21 and splitcore 41. The operator allows electrical conductor W to be accommodatedin cutouts 213 a, 215 a, and 223 a of case 21. Electrical conductor W issupported by cutouts 213 a, 215 a, and 223 a, and is disposed on theopen end side of split core 41.

Next, the operator assembles case 22 to case 21 supporting electricalconductor W. In the assembling, the operator engages fitting protrusions228 a and 228 b provided on upper walls 224 of case 22 with locking part212 of case 21, thus assembling case 21 and case 22. Joining surface 411of split core 41 is joined with joining surface 421 of split core 42,and joining surface 412 of split core 41 is joined with joining surface431 of split core 43 inside case 21 and case 22, thereby providingcurrent sensor 10.

When positions of cases 21 and 22 are relatively deviated due to amechanical impact, such as dropping and transfer, applied to currentsensor 10, split cores 41, 42, and 43 may crack and chip at joiningsurfaces 411 and 412 of split core 41 and joining surfaces 421 and 431of split cores 42 and 43 that contact each other but are not bonded toeach other. In current sensor 10, as described above, three fittingprotrusions 228 a and 228 b are engaged with locking part 212 torestrict relative positional deviation of case 21 and case 22 and fixcases 21 and 22 to each other while being assembled. As a result,relative deviation of split cores 41, 42, and 43 is prevented to avoidchipping of split cores 41, 42, and 43.

In accordance with the embodiment, the joining surfaces are simplycontact each other to join without bonding the joining surfaces.However, the joining surfaces may be bonded to each other with magneticadhesive, or the joining surfaces may be welded to each other. Evenafter bonding or welding, the joining surfaces before bonding or weldingcan be identified by analyzing a bonding mark or a welding mark. Whenjoining surfaces simply contact each other, the core may be easilydisassembled by separating split cores. Therefore, operability duringmaintenance, for example, can be increased.

Effects

As described above, current sensor 10 in accordance with the embodimentincludes core 40 through which electrical conductor W passes, and coil60 wound on core 40. Split cores 41, 42, and 43 are joined to oneanother so as to constitute to form core 40. Core 40 substantially hasthe C-shape partially provided with gap S therein. The pairs of joiningsurfaces 411, 412, 421, and 431 of cores 41, 42, and 43 (specifically,the pair of joining surface 411 and joining surface 421, and the pair ofjoining surface 412 and joining surface 431) are parallel to facingdirection DX of other end surfaces 422 and 432, which are the pair ofend surfaces of core 40 forming gap S.

As a result of studies, the inventors of the present disclosure havefound that the boundary part may be ignored by providing, in a part ofcore 40, gap S extremely larger than boundary parts of split cores 41,42, and 43. FIG. 7 is a graph showing a BH curve of ferrite, a materialof core 40 in accordance with the embodiment.

A core without gap S is prepared as a comparative example. The core ofthe comparative example has a configuration same as core 40 inaccordance with the embodiment except that the comparative example doesnot have gap S. A magnetic flux density of the core of the comparativeexample is value L21 ranging from 455 mT to 465 mT. In this range, a BHcurve changes in a curve, and inclination of tangent L22 of the BH curveis small. Therefore, magnetic saturation of the core in the comparativeexample may occur at the magnetic flux density of about 0.5 T.

On the other hand, a magnetic flux density of core 40 having gap S inaccordance with the embodiment is value L23 ranging from 180 mT to 190mT. Therefore, the BH curve is linear, and the magnetic flux densitychanges in region R1 that has large inclination. As a result, core 40suppresses magnetic saturation.

FIG. 8 shows comparison between output V40 of core 40 in accordance withthe embodiment and output V1 of the core of the comparative example.Waveforms of outputs V40 and V1 are generated when a sinusoidal currentwith amplitude of 15 A and a frequency of 5 kHz is applied to electricalconductor W. As shown in FIG. 8, the waveform of the output of the coreof the comparative example is significantly distorted at the peak. Thisis due to occurrence of magnetic saturation. On the other hand, thewaveform of output V40 of core 40 in accordance with the embodiment isnot distorted at the peak. This means that magnetic saturation issuppressed in core 40 in accordance with the embodiment, compared withthe core of the comparative example.

In current sensor 10 in accordance with the embodiment, the pairs ofjoining surfaces 411, 412, 421, and 431 of split cores 41, 42, and 43forming core 40 are parallel to facing direction DX in which the pair ofother end surfaces 422 and 432 face each other and forming gap S of core40. This configuration allows distance LX of gap S to be adjusted infacing direction DX by sliding the pairs of joining surfaces 411, 412,421, and 431 of split cores 41, 42, and 43 with respect to one another.

FIG. 9 is a graph showing a relationship of gap S of core 40 and outputV40 of current sensor 10 in accordance with the embodiment. As shown inFIG. 9, as distance LX of gap S increases, sensitivity tends todecrease. However, a decrease of sensitivity saturates after thedistance exceeds a certain length. In other words, the desiredsensitivity characteristic can be obtained just by adjusting distance LXof gap S without being affected by a faint gap in the boundary parts ofsplit cores 41, 42, and 43.

The above shows that the desired sensitivity characteristic can beachieved even when the boundary part exists in core 40 in current sensor10 in accordance with the embodiment.

Various sensitivity characteristics can be achieved by adjustingdistance LX of gap S although the same type of core is used.Accordingly, a common component may be applied to other types of currentsensor.

Adjustment of gap S may result in deviated arrangement with a leveldifference of at least split core 42 or split core 43 with respect tosplit core 41. FIG. 10A and FIG. 10B show the state of arrangement witha level difference between at least split core 42 or split core 43 andsplit core 41 in accordance with the embodiment. Specifically, in FIG.10A, both split core 42 and split core 43 are deviated in widthdirection X with respect to split core 41. In FIG. 10B, both split core42 and split core 43 are deviated in thickness direction Y with respectto split core 41. The inventor has changed a degree of deviation ofsplit core 42 and split core 43 with respect to split core 41, andobtained a current-output line for each deviation. FIG. 11 shows thecurrent-output line for each degree of deviation of core 40 inaccordance with the embodiment. Output V41 is obtained under thecondition that core 40 is not deviated. Output V42 is obtained under thecondition that both split core 42 and split core 43 are deviated withrespect to split core 41 by 0.5 mm in width direction X, and output V43is obtained under the condition of the deviation by 1.0 mm in widthdirection X. FIG. 11 also shows output V44 obtained under the conditionthat both split core 42 and split core 43 are deviated with respect tosplit core 41 by 0.5 mm in thickness direction Y and output V45 obtainedunder the condition of the deviation by 1.0 mm in thickness direction Y.As shown in FIG. 11, the current-output lines are almost the same in allof these conditions. In other words, there is no influence on thesensitivity characteristic of current sensor 10 even when at least splitcore 42 or split core 43 is deviated with a level difference inarrangement with split core 41 due to adjustment of gap S.

Distance LX of gap S may also be determined with reference to parametersof core 40. Parameters for determining distance LX of gap S are, forexample, the number of turns of electrical conductor W, across-sectional area of electrical conductor W, a shape of core 40, adistance from electrical conductor W to core 40, and a material of core40. The material of core 40 other than ferrite may be, e.g., Ni-Zn basedmaterial, Mn-Zn based material, or iron based material.

The number of split cores 41, 42, and 43 is three or more, and the pairsof joining surfaces 411, 412, 421, and 431 of each pair of split coresare parallel to facing direction DX.

Three or more split cores 41, 42, and 43 allow the inside of C-shapedcore 40 to widely open during assembly, and facilitate electricalconductor W be disposed inside C-shaped core 40.

The pairs of joining surfaces 411, 412, 421, and 431 of each pair ofsplit cores (the pair of split core 41 and split core 42 and the pair ofsplit core 41 and split core 43) are parallel to facing direction DX.This configuration allows distance LX of gap S to be adjusted just bysliding each of the pairs of joining surfaces 411, 412, 421, and 431 ofthe pairs of split cores.

Current sensor 10 includes non-magnetic bobbin 50 having coil 60 woundthereon. Bobbin 50 contacts and stops the pair of end surfaces (otherend surfaces 422 and 432) of core 40, and surrounds gap S.

Non-magnetic bobbin 50 having coil 60 wound thereon contacts and stopsthe pair of end surfaces of core 40. This configuration allows gap Safter adjustment to be stably retained. This configuration may eliminatea dedicated component for retaining distance LX of gap S, accordinglysuppressing an increase of the number of components. In addition, bobbin50 made of a non-magnetic body does not affect current detection.

When coil 60 is directly wound on core 40 to surround gap S, a windingwork is difficult due to gap S. However, coil 60 is wound onnon-magnetic bobbin 50 and bobbin 50 surrounds gap S to enhance theefficiency of work.

Current sensor 10 includes case 21 accommodating split core 41, which isone split core of plural split cores 41, 42, and 43, and case 22accommodating split cores 42 and 43, which are one or more other splitcores of the plural split cores 41, 42, and 43. Case 21 and case 22 areassembled together, and one split core 41 is fixed onto other splitcores 42 and 43.

As a result, positions of the plurality of split cores 41, 42, and 43inside case 21 and case 22 are unlikely deviated from each other afterassembling. Accordingly, distance LX of gap S in core 40 is stabilizedfor a long period of time to retain the sensitivity characteristic ofcurrent sensor 10 for a long period of time.

The plural split cores 41, 42, and 43 are joined to form core 40.

By assembling the plurality of split cores 41, 42, and 43 to surroundelectrical conductor W and form core 40, electrical conductor W can beeasily disposed inside to pass through C-shaped core 40.

MODIFIED EXAMPLES

The configuration of the core is not limited to that described in theabove exemplary embodiment. Modified examples of the core will bedescribed below centering on a difference with the above exemplaryembodiment. In the following description, components same as those ofthe above exemplary embodiment will be given the same reference marks,and the description thereof may be omitted.

Modified Example 1

In the above embodiment, current sensor 10 includes core 40 composed ofthree split cores 41, 42, and 43. A current sensor of modified example 1includes core 40A composed of two split cores 44 and 45. FIG. 12 is aplan view of core 40A of modified example 1. FIG. 12 corresponds to FIG.6.

As shown in FIG. 12, core 40A is composed of two split cores 44 and 45.Split core 44 has gap Sa therein at a lower part of the rectangularframe shape in the positive direction of the X axis. One end surface 441out of a pair of end surfaces 441 and 442 of split core 44 directed inthe positive direction of the X axis, and another end surface 442 out ofthe pair of end surfaces 441 and 442 of split core 44 directed downward,i.e., in the negative direction of the Z-axis. One end surface 441 is aplane parallel to the YZ plane. Another end surface 442 is a planeparallel to the XY plane. One end surface 441 is a joining surface to bejoined with other split core 45.

Split core 45 substantially has an L-shape. One end surface 451 of splitcore 45 is a joining surface to be joined with end surface 441 of splitcore 44. One end surface 451 of split core 45 is a plane parallel to theYZ plane. One end surface 451 is joined with tip surface 441 of splitcore 44 while another end surface 452 of split core 45 is directedupward. Other end surface 452 of split core 45 is a plane parallel tothe XY plane.

Gap Sa is provided between end surface 442 of split core 44 and anotherend surface 452 of split core 45. A pair of end surfaces (end surface442 and another end surface 452) that form gap Sa face each other acrossgap Sa in facing direction DZ of the Z axis. Distance LZ (a length inthe Z-axis direction) of gap Sa is adjusted before assembly to achieve adesired sensitivity characteristic. As described above, both end surface441 of split core 44 and one end surface 451 of split core 45 are planesparallel to the YZ plane. Therefore, the joining surfaces (end surface441 and one end surface 451) of split cores 44 and 45 are slidable withrespect to each other to move split core 45 and adjust the position ofanother end surface 452 of split core 45 in the Z-axis direction. As aresult, distance LZ of gap Sa can be adjusted.

In core 40A of modified example 1, coil 60 is wound around an upper partof split core 45. Coil 60 may be directly wound around the upper part ofsplit core 45 or wound indirectly via the bobbin around the upper partof split core 45.

Modified Example 2

In the above embodiment, current sensor 10 includes core 40 with gap Sprovided at the center of the upper frame part of the frame shape. Acurrent sensor of modified example 2 includes core 40B with gap Sb atthe center of a lower frame part of the frame shape. FIG. 13 is a planview of core 40B of modified example 2. FIG. 13 corresponds to FIG. 6.

Core 40B substantially has a C-shape having gap Sb therein at the centerof the lower frame part of the rectangular frame shape in the plan view.Core 40B has a configuration of core 40 with id reversed up and down,and its structure is equivalent to core 40. In core 40B of modifiedexample 2, coil 60 is wound on an upper part of split core 41. Coil 60may be directly wound on the upper part of split core 41 or woundindirectly via the bobbin around the upper part of split core 41.

Position of Coil

In current sensor 10, another electrical conductor different fromelectrical conductor W may be disposed outside core 40. This electricalconductor may degrade accuracy of detection of a current in electricalconductor W. However, by disposing coil 60 at an appropriate positionwith respect to core 40, an influence of other electrical conductor canbe suppressed to enhance accuracy of current detection of electricalconductor W.

FIG. 14A illustrates an influence of other electrical conductors W2, W3,W4, and W5 on core 40A of modified example 1. FIG. 14B illustrates aninfluence of other electrical conductors W2, W3, W4, and W5 on core 40Bof modified example 2. FIG. 14C illustrates an influence of otherelectrical conductors W2, W3, W4, and W5 on core 40 in accordance withthe embodiment. As shown in FIGS. 14A to 14C, other electrical conductorW2 is disposed above cores 40, 40A, and 40B. Other electrical conductorW3 is disposed in the positive direction of the X axis of cores 40, 40A,and 40B. Other electrical conductor W4 is disposed below cores 40, 40A,and 40B. Other electrical conductor W5 is disposed in the negativedirection of the X axis of cores 40, 40A, and 40B.

Each graph in FIGS. 14A to 14C shows an influence of other electricalconductors W2 to W5 on detection of current flowing through electricalconductor W when gaps S, Sa, and Sb are changed from 0 mm to 3 mm. Aninfluence of other electrical conductor W5 is equivalent to otherelectrical conductor W3 of modified example 2 and the embodiment, andthus electrical conductor W5 is omitted. A sensor output of −20 dB orgreater indicates that other electrical conductor has a significantinfluence.

In modified example 1, electrical conductors W2 to W4 other thanelectrical conductor W5 provide values greater than −20 dB. It isapparent that a current detection of electrical conductor W is affected.In modified example 2, electrical conductors W2 and W4 other thanelectrical conductor W3 provide values greater than −20 dB. It isapparent that a current detection of electrical conductor W is affected.These influences occur due to entry of magnetic flux from externalelectrical conductors W2 to W5 through spaces Sa and Sb.

On the other hand, in accordance with the embodiment, the output is −20dB or less in all of other electrical conductors W2 to W4. Fluctuationis also small. This is because coil 60 is wound at a positionsurrounding gap S in core 40, and coil 60 blocks the magnetic flux fromexternal electrical conductors W2 to W5 toward gap S. The influence ofthe magnetic flux can thus be suppressed. In other words, core 40 inaccordance with the embodiment is preferable from the view ofsuppressing the influence of other electrical conductors W2 to W5.

An influence of other electrical conductors W2, W3, W4, and W5 when coil60 is disposed at different positions in cores 40, 40A, and 40B ofmodified examples 1 and 2 will be described below.

FIGS. 15 to 17 illustrate the state of cores 40, 40A, and 40B inconditions and sensor output in the conditions. Sensor output in eachcondition shows an influence of other electrical conductors W2 to W4 ondetection of current flowing through electrical conductor W. In a graphshowing the sensor output, a smaller output (longer bar graph) signifiesa smaller influence on current detection of electrical conductor W.

As shown in FIG. 15, coil 60 is wound at an upper part of core 40B inmodified example 2 in condition A. In condition B, coil 60 is wound atan upper part of core 40 in the exemplary embodiment. In condition C,coil 60 is wound at an upper part of core 40A in modified example 1. Inother words, gaps Sa and Sb are fully exposed from coil 60 in conditionsA and C, but gap S is entirely covered with coil 60 in condition B.

As shown in FIG. 15, condition B provides a smaller influence of any ofother electrical conductors W2, W3, and W4 than conditions A and C.

As shown in FIG. 16, in condition D, coil 60 is wound on a lower part ofcore 40B of modified example 2. In condition E, coil 60 is wound on alower part of core 40 in accordance with the embodiment. In condition F,coil 60 is wound on a lower part of core 40A of modified example 1. Inother words, gaps S and Sb are entirely exposed from coil 60 inconditions E and F, but gap Sa is entirely covered with coil 60 incondition D.

As shown in FIG. 16, condition D provides a larger influence of otherelectrical conductor W3 but an influence of other electrical conductorsW2 and W4 is smaller than condition E. In addition, condition D providesa smaller influence of all of other electrical conductors W2, W3, and W4than condition F. Therefore, as a whole, condition D provides a smallerinfluence of other electrical conductors W2, W3, and W4 than conditionsE and F.

As shown in FIG. 17, coil 60 is wound on the center on the positive sideof X axis of core 40B of modified example 2 in condition G. In conditionH, coil 60 is wound on the center part on the positive side of X axis ofcore 40 in accordance with the embodiment. In condition I, coil 60 iswound on the center part on the positive side of X axis of coil 40A ofmodified example 1. In other words, gaps S and Sa in conditions G and Hare entirely exposed from coil 60, but gap Sb in condition I is entirelycovered with coil 60.

As shown in FIG. 17, condition I provides a smaller influence of any ofother electrical conductors W2, W3, and W4 than conditions G and H.

Conditions B, E, and H related to core 40 in accordance with theembodiment will be focused below. Condition B in which gap S issurrounded by coil 60 provides a larger influence of other electricalconductor W3 but a smaller influence of other electrical conductors W2and W4 than condition E. Condition B provides a smaller influence of allof other electrical conductors W2, W3, and W4 than condition H.Therefore, as a whole, condition B provides a smaller influence ofelectrical conductors W2, W3, and W4 than conditions E and H.

Conditions A, D, and G related to core 40A of modified example 1 will befocused below. Condition D in which gap Sa is surrounded by coil 60provides a smaller influence of any of other electrical conductors W2,W3, and W4 than conditions A and G.

Conditions C, F, and I related to core 40B of modified example 2 will befocused below. Condition I in which gap Sb is surrounded by coil 60receives provides a larger influence of other electrical conductor W3but a smaller influence of other electrical conductors W2 and W4 thancondition C. It is apparent that condition I provides a smallerinfluence of all of other electrical conductors W2, W3, and W4 thancondition F. Therefore, as a whole, condition I provides a smallerinfluence of other electrical conductors W2, W3, and W4 than conditionsC and F.

As described above, current sensor 10 includes core 40 (40B, 40B)through which electrical conductor W passes, and coil 60 wound on core40 (40A, 40B). Core 40 (40A, 40B) has a C-shape and gap S, Sa, or Sb isprovided in a part of the C-shape. Coil 60 is wound at a positionsurrounding gap S (Sa, Sb).

Coil 60 wound on the position surrounding gap S (Sa, Sb) of core 40(40A, 40B) blocks magnetic flux from external electrical conductors W2to W5 toward gap S (Sa, Sb). This configuration suppresses an influenceof the magnetic flux, i.e., external noise.

The pair of end surfaces (other end surfaces 422 and 432, end surface442, other end surface 452) of core 40 (40A, 40B) that form gap S (Sa,Sb) is disposed inside coil 60.

As a result, coil 60 covers both end parts of gap S (Sa, Sb). Therefore,coil 60 reliably blocks magnetic flux from external electricalconductors W2 to W5 toward gap S (Sa, Sb). This configuration suppressesan influence of magnetic flux from external electrical conductors W2 toW5 reliably accordingly.

Another Exemplary Embodiment

FIG. 18 is a perspective view of another current sensor 510 inaccordance with the embodiment. FIG. 19 is a sectional view of currentsensor 510 along line XIX-XIX shown in FIG. 18. FIG. 20 is a sectionalview of current sensor 510 taken along line XX-XX shown in FIG. 18. InFIGS. 18 to 20, components identical to those of current sensor 10 shownin FIGS. 1 to 5 are denoted by the same reference numerals. Currentsensor 510 includes housing 520 and sensor unit accommodated in housing520.

FIG. 21 is a perspective view of housing 520. In FIG. 21, componentsidentical to those of the housing of current sensor 10 shown in FIG. 1and FIG. 2 are denoted by the same reference numerals. Housing 520includes cases 21 and 22 divided in the Z-axis direction, and hinge 551that connects cases 21 and 22 to each other. Hinge 551 connects one ofthe pair of lower walls 214 of main body 211 of case 21 with one of thepair of upper walls 224 of main body 221 of case 22.

Case 21 includes main body 211 and locking part 212 to be engaged withcase 22. Main body 211 has a box shape having space 21 a opening in thepositive direction of the Z axis Locking part 212 is provided at aposition on the opposite side of hinge 551. Locking part 212 is providedon the other of the pair of lower walls 214 of main body 211 of case 21.Split core 41 that is a part of sensor unit 530 is fitted in and fixedbetween inner walls 215.

Case 22 has a box shape having space 22 s opening in the negativedirection of the Z axis. Case 22 includes a pair of upper walls 223facing each other in the Y-axis direction, a pair of upper walls facingeach other in the X-axis direction, and bottom plate 229. Upper walls223 and 224 are connected to each other and extending from bottom plate229 in the negative direction of the Z axis. Upper walls 223 and 224 andbottom plate 229 surround space 22 s.

Fitting protrusion 228 a is provided on other outer surface of the pairof upper walls 224 of case 22.

Locking part 212 of case 21 is extended from the outer surface of lowerwall 214 in the positive direction of the Z axis. Locking part 212substantially has a U-shape. Locking part 212 is engaged with fittingprotrusion 228 a of case 22 by relatively rotating case 21 about hinge551 with respect to case 22, and case 21 and case 22 are assembledtogether and fixed to each other.

In current sensor 10 shown in FIG. 3, split cores 42 and 43 contactinternal bottom part 53 of bobbin 50, and are also press-fitted intospace 50 s of bobbin body 51 to be firmly fixed onto bobbin 50. As shownin FIG. 19, in current sensor 510, split cores 42 and 43 contactinternal bottom part 53, but split cores 42 and 43 are accommodated inspace 50 a with clearance 50 t from bobbin body 51. Therefore, splitcores 42 and 43 are not fixed to bobbin 50 before being accommodated incase 22, but split core 42, split core 43, and bobbin 50 are positionedand firmly fixed in case 22 to retain the shape of sensor unit 530.

As shown in FIGS. 18 to 20, in current sensor 510, inner lid 531 thatcovers bobbin 50 is provided on an opening of case 22. Inner lid 53prevents conductive or magnetic foreign particles from entering insidecase 22 and protects coil 60 to prevent any influence on detectionaccuracy of current sensor 530.

In current sensor 510, as shown in FIG. 19 and FIG. 21, case 22 includesrib 610 that protrudes from main body 221 toward space 22 s to positionsplit core 41 (42). Rib 610 positions split cores 41 and 42 with respectto case 22 and bobbin 50. When current sensor 510 is assembled, splitcore 42, split core 43, and bobbin 50 are positioned and firmly fixedwith respect to case 22 by press-fitting and inserting split cores 41and 42 inserted to space 50 s of bobbin 50 into case 22. Duringinsertion, split cores 41 and 42 may scrape case 22 and generate scrapedparticles. The particles may enter between split core 41 (42) and facingsurface 612 a of rib 610. The particles entering between split core 41(42) and facing surface 612 a of rib 610 may displace split core 41 (42)with respect to rib 610 and prevent the shape of core 40 from beingretained, or prevent locking part 212 of case 21 from reaching fittingprotrusion 228 a on case 22, consequently preventing engagement.

To wipe out the above problem in current sensor 510, rib 610 includesbase 611 that protrudes from main body 221 toward space 22 s, andpositioner 612 that extends from base 611 to split core 41 (42).Positioner 612 has facing surface 612 a that faces and contacts splitcore 41 (42). Positioner 612 is located apart from main body 221 acrossslit 613 extended from facing surface 612 a. This configuration allowsthe scraped particles at inserting split cores 41 and 42 into case 22 tomove through slit 613 to prevent the particles from being left betweensplit core 41 (42) and facing surface 612 a of rib 610.

In current sensor 510, case 21 includes protrusions 230 a and 230 bconfigured to be fitted inside space 22 s so that case 21 contacts mainbody 221 of case 22 by assembling case 21 and case 22 together.Protrusion 230 a protrudes from lower wall 214 of case 21 that does nothave hinge 551 and is on the opposite side of hinge 551. Protrusion 230b extends from bottom plate 219 of case 21. Protrusions 230 a and 230 bcontact main body 221, particularly upper walls 223, of case 22 byassembling case 21 and case 22 together. This configuration preventsrelative deviation of cases 21 and 22, particularly the rotation ofcases 21 and 22 in directions opposite to each other about hinge 551.With this configuration, similarly to current sensor 10, cases 21 and 22are assembled together and fixed to each other even when a mechanicalimpact, such as dropping and transfer, is applied. As a result, relativedeviation of split cores 41, 42, and 43 are prevented and chipping ofsplit cores 41, 42, and 43 is prevented.

FIG. 23 is an enlarged sectional view of current sensor 510 in FIG. 19.Current sensor 510 may preferably further include cushion 541 betweenmain body 211 of case 21 and split core 41. Cushion 541 contacts lowerwall 214 and split core 41 between split core 41 and in main body 211,particularly lower wall 214. This configuration reliably positions andfixes split core 41 with respect to case 21 to prevent cracking of splitcores 41, 42, and 43.

FIG. 23 is a perspective view of another sensor unit 530 of currentsensor 510. In FIG. 23, components identical to those of sensor unit 30in shown FIG. 4 are denoted by the same reference numerals. Byassembling case 21 and case 22 together, joining surface 411 of splitcore 41 is joined with joining surface 421 of split core 42, and joiningsurface 412 of split core 41 is joined with joining surface 431 of splitcore 43. Both ends 411 a of joining surface 411 of split core 41 in theY-axis direction are chamfered. However, either one of both ends 411 amay not be chamfered. Both ends 412 a of joining surface 412 of splitcore 41 in the Y-axis direction are chamfered. However, either one ofboth ends 412 a may not be chamfered. This configuration prevents edgesof split cores 41, 42, and 43 from directly contacting one another evenwhen a mechanical impact, such as dropping and transfer, is applied,thereby preventing chipping of split cores 41, 42, and 43.

FIG. 24 is a perspective view of still another sensor unit 630 ofcurrent sensor 510. In FIG. 24, components identical to those of sensorunit 530 shown in FIG. 23 are denoted by the same reference numerals.Both ends 421 a of joining surface 421 of split core 42 in the Y-axisdirection are chamfered. However, either one of both ends 421 a may notbe chamfered. Both ends 431 a of joining surface 431 of split core 43 inthe Y-axis direction are chamfered. However, either one of both ends 431a may not be chamfered. This configuration prevents edges of split cores41, 42, and 43 from directly contacting one another even when amechanical impact, such as dropping and transfer, is applied, therebypreventing chipping of split cores 41, 42, and 43.

Others

The exemplary embodiments and modified examples of the current sensor inthe present disclosure are described above. However, the presentdisclosure is not limited to the above exemplary embodiments andmodified examples.

In the above exemplary embodiments, the core split in two or three isgiven as an example. However, the core may be split to four or more.Still more, when suppression of an influence of other electricalconductors W2 to W5 is the only consideration, which means adjustment ofdistance LX of gap S is not considered, the core may not be split.

Furthermore, the present disclosure includes a mode obtained by applyingvarious modifications conceived by those skilled in the art to theexemplary embodiments, and a mode realized by arbitrarily combiningcomponents and functions in the exemplary embodiments and the modifiedexamples without departing from the gist of the present disclosure.

REFERENCE MARKS IN THE DRAWINGS

-   10 current sensor-   20 housing-   21 case (first case)-   22 case (second case)-   30 sensor unit-   40, 40A, 40B core-   41, 42, 43, 44, 45 split core-   50 bobbin-   51 bobbin body-   52 flange-   53 internal bottom part-   60 coil-   211 main body-   212 locking part-   213 lower wall-   213 a, 215 a, 223 a cutout-   214 lower wall-   215 inner wall-   221 main body-   223 upper wall-   224 upper wall-   224 a protrusion-   224 b regulating projection-   228 a, 228 b fitting protrusion-   411, 412, 421, 431 joining surface-   422, 432, 452 end surface-   441, 442 tip surface-   451 one end surface-   510 current sensor-   520 housing-   530 sensor unit-   630 sensor unit-   W electrical conductor

1. A current sensor configured to detect a current flowing through anelectrical conductor, the current sensor comprising: a core having ahollow therein configured to allow the electrical conductor to passthrough the hollow; and a coil wound around the core, wherein the coresubstantially has a C-shape having a gap connected to the hollow, thecore has a pair of end surfaces facing each other in a facing directionacross the gap, the core includes a plurality of split cores joined toone another, and each pair of split cores of the plurality of splitcores adjacent to each other have respective joining surfaces joined toeach other, the respective joining surfaces of the each pair of splitcores being parallel to the facing direction.
 2. The current sensoraccording to claim 1, wherein a number of the plurality of split coresis equal to or larger than three.
 3. The current sensor according toclaim 1, further comprising a bobbin having the coil wound thereon, thebobbin being made of non-magnetic material, wherein the bobbin contactsthe pair of end surfaces of the core to stop the pair of end surfaces ofthe core, and surrounds the gap.
 4. The current sensor according toclaim 1, further comprising a housing which includes: a first caseincluding a first main body having a space therein accommodating a firstsplit core of the plurality of split cores therein; and a second caseincluding a second main body having a space therein accommodating asecond split core of the plurality of split cores therein, wherein thefirst split core and the second split core are fixed to each other whilethe first case and the second case are assembled together.
 5. Thecurrent sensor according to claim 4, wherein the second case furtherincludes a rib protruding from the second main body toward the space andpositions the second split core, the rib includes: a base protrudingfrom the second main body toward the space; and a positioner extendedfrom the base toward the second split core, the positioner having asurface facing the second split core, the surface of the positionerpositioning the second split core thereon, and the positioner of the ribis apart from the second main body via a slit extended from the surfaceof the positioner.
 6. The current sensor according to claim 5, whereinthe housing further includes a hinge connecting the first case with thesecond case.
 7. The current sensor according to claim 5, wherein thefirst case includes a protrusion, the protrusion of the first case beingconfigured to enter in the space of the second main body and contact thesecond main body of the second case while the first case and the secondcase are assembled together.
 8. The current sensor according to claim 4,further comprising a cushion provided between the first main body andthe first split core.
 9. The current sensor according to claim 4,wherein a joining surface of the first split core is joined to a joiningsurface of the second split core while the first case and the secondcase are assembled together, and an end of the joining surface of thefirst split core is chamfered.
 10. The current sensor according to claim9, wherein both ends of the joining surface of the first split core arechamfered.
 11. The current sensor according to claim 9, wherein an endof the joining surface of the second split core is chamfered.
 12. Thecurrent sensor according to claim 11, wherein both ends of the joiningsurface of the second split core are chamfered.
 13. The current sensoraccording to claim 7, wherein the joining surface of the first splitcore is parallel to the facing direction.
 14. The current sensoraccording to claim 8, wherein the joining surface of the first splitcore is parallel to the facing direction.
 15. The current sensoraccording to claim 9, wherein the joining surface of the first splitcore is parallel to the facing direction.